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Marc Fournier - One of the best experts on this subject based on the ideXlab platform.
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Polyphase ductile/brittle deformation along a major tectonic boundary in an ophiolitic nappe, Alpine Corsica: Insights on subduction zone intermediate-depth asperities
Journal of Structural Geology, 2017Co-Authors: Remi Magott, Olivier Fabbri, Marc FournierAbstract:In an ophiolitic nappe of Alpine Corsica, a major fault zone superimposes Metagabbro over serpentinite and peridotite. Ductile and brittle deformation structures are observed in the fault damage zones. In the Metagabbro damage zone, early deformation culminates in blueschist or eclogite facies conditions and consists of west-verging mylonitization alternating with pseudotachylyte-forming faulting with undetermined vergence. This early deformation is likely coeval with west-verging seismic (pseudotachylyte-forming) reverse faulting in the footwall peridotite or with aseismic distributed cataclastic deformation of footwall serpentinite. These early events (aseismic mylonitization or distributed cataclasis and seismic faulting) are interpreted as reverse faulting/shear in an east-dipping subducting oceanic lithosphere in Cretaceous to Eocene times. Late deformation events consist of ductile shear and seismic faulting having occurred under retrograde greenschist conditions. Kinematics of the ductile shear is top-to-the-east. These events are interpreted as the result of syn-to post-collision extension of Alpine Corsica in Eocene to Miocene times. The heterogeneous distribution of pseudotachylyte veins along the fault zone (abundant at peridotite-Metagabbro interfaces, rare or absent at serpentinite-Metagabbro interfaces) is interpreted as the consequence of contrasted frictional properties of the rocks in contact. High-friction peridotite-Metagabbro contacts could correspond to asperities whereas low-friction serpentinite-Metagabbro contacts could correspond to creeping zones.
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polyphase ductile brittle deformation along a major tectonic boundary in an ophiolitic nappe alpine corsica insights on subduction zone intermediate depth asperities
Journal of Structural Geology, 2017Co-Authors: Remi Magott, Olivier Fabbri, Marc FournierAbstract:In an ophiolitic nappe of Alpine Corsica, a major fault zone superimposes Metagabbro over serpentinite and peridotite. Ductile and brittle deformation structures are observed in the fault damage zones. In the Metagabbro damage zone, early deformation culminates in blueschist or eclogite facies conditions and consists of west-verging mylonitization alternating with pseudotachylyte-forming faulting with undetermined vergence. This early deformation is likely coeval with west-verging seismic (pseudotachylyte-forming) reverse faulting in the footwall peridotite or with aseismic distributed cataclastic deformation of footwall serpentinite. These early events (aseismic mylonitization or distributed cataclasis and seismic faulting) are interpreted as reverse faulting/shear in an east-dipping subducting oceanic lithosphere in Cretaceous to Eocene times. Late deformation events consist of ductile shear and seismic faulting having occurred under retrograde greenschist conditions. Kinematics of the ductile shear is top-to-the-east. These events are interpreted as the result of syn-to post-collision extension of Alpine Corsica in Eocene to Miocene times. The heterogeneous distribution of pseudotachylyte veins along the fault zone (abundant at peridotite-Metagabbro interfaces, rare or absent at serpentinite-Metagabbro interfaces) is interpreted as the consequence of contrasted frictional properties of the rocks in contact. High-friction peridotite-Metagabbro contacts could correspond to asperities whereas low-friction serpentinite-Metagabbro contacts could correspond to creeping zones.
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subduction zone intermediate depth seismicity insights from the structural analysis of alpine high pressure ophiolite hosted pseudotachylyte corsica france
Journal of Structural Geology, 2016Co-Authors: Remi Magott, Olivier Fabbri, Marc FournierAbstract:Pseudotachylyte in the Cima di Gratera ophiolite, Alpine Corsica, is distributed in the peridotite unit and in the overlying Metagabbro unit and was formed under blueschist to eclogite metamorphic facies conditions, corresponding to a 60–90 km depth range. Peridotite pseudotachylyte is clustered in fault zones either beneath the tectonic contact with overlying Metagabbros or at short distance from it. Fault zones are either parallel to the contact or make an angle of 55° to it. Displacement sense criteria associated with fault veins indicate top-to-the-west or top-to-the-northwest reverse senses. Cataclasite flanking most veins was formed before or coevally with frictional melting and likely mechanically weakened the peridotite, facilitating subsequent seismic rupture. In the basal part of the Metagabbro unit, post-mylonitization pseudotachylyte can be distinguished from pre-mylonitization pseudotachylyte formed earlier. In the equant Metagabbro above the mylonitic sole, only one episode of pseudotachylyte formation can be identified. Kinematics associated with Metagabbro pseudotachylyte remain unknown. The geometry and kinematics of the pseudotachylyte veins from the peridotite unit and to a lesser extent from the Metagabbro unit are similar to modern seismic ruptures of the upper parts of the Wadati-Benioff zones such as in the Pacific plate beneath NE Japan.
Remi Magott - One of the best experts on this subject based on the ideXlab platform.
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Polyphase ductile/brittle deformation along a major tectonic boundary in an ophiolitic nappe, Alpine Corsica: Insights on subduction zone intermediate-depth asperities
Journal of Structural Geology, 2017Co-Authors: Remi Magott, Olivier Fabbri, Marc FournierAbstract:In an ophiolitic nappe of Alpine Corsica, a major fault zone superimposes Metagabbro over serpentinite and peridotite. Ductile and brittle deformation structures are observed in the fault damage zones. In the Metagabbro damage zone, early deformation culminates in blueschist or eclogite facies conditions and consists of west-verging mylonitization alternating with pseudotachylyte-forming faulting with undetermined vergence. This early deformation is likely coeval with west-verging seismic (pseudotachylyte-forming) reverse faulting in the footwall peridotite or with aseismic distributed cataclastic deformation of footwall serpentinite. These early events (aseismic mylonitization or distributed cataclasis and seismic faulting) are interpreted as reverse faulting/shear in an east-dipping subducting oceanic lithosphere in Cretaceous to Eocene times. Late deformation events consist of ductile shear and seismic faulting having occurred under retrograde greenschist conditions. Kinematics of the ductile shear is top-to-the-east. These events are interpreted as the result of syn-to post-collision extension of Alpine Corsica in Eocene to Miocene times. The heterogeneous distribution of pseudotachylyte veins along the fault zone (abundant at peridotite-Metagabbro interfaces, rare or absent at serpentinite-Metagabbro interfaces) is interpreted as the consequence of contrasted frictional properties of the rocks in contact. High-friction peridotite-Metagabbro contacts could correspond to asperities whereas low-friction serpentinite-Metagabbro contacts could correspond to creeping zones.
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polyphase ductile brittle deformation along a major tectonic boundary in an ophiolitic nappe alpine corsica insights on subduction zone intermediate depth asperities
Journal of Structural Geology, 2017Co-Authors: Remi Magott, Olivier Fabbri, Marc FournierAbstract:In an ophiolitic nappe of Alpine Corsica, a major fault zone superimposes Metagabbro over serpentinite and peridotite. Ductile and brittle deformation structures are observed in the fault damage zones. In the Metagabbro damage zone, early deformation culminates in blueschist or eclogite facies conditions and consists of west-verging mylonitization alternating with pseudotachylyte-forming faulting with undetermined vergence. This early deformation is likely coeval with west-verging seismic (pseudotachylyte-forming) reverse faulting in the footwall peridotite or with aseismic distributed cataclastic deformation of footwall serpentinite. These early events (aseismic mylonitization or distributed cataclasis and seismic faulting) are interpreted as reverse faulting/shear in an east-dipping subducting oceanic lithosphere in Cretaceous to Eocene times. Late deformation events consist of ductile shear and seismic faulting having occurred under retrograde greenschist conditions. Kinematics of the ductile shear is top-to-the-east. These events are interpreted as the result of syn-to post-collision extension of Alpine Corsica in Eocene to Miocene times. The heterogeneous distribution of pseudotachylyte veins along the fault zone (abundant at peridotite-Metagabbro interfaces, rare or absent at serpentinite-Metagabbro interfaces) is interpreted as the consequence of contrasted frictional properties of the rocks in contact. High-friction peridotite-Metagabbro contacts could correspond to asperities whereas low-friction serpentinite-Metagabbro contacts could correspond to creeping zones.
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subduction zone intermediate depth seismicity insights from the structural analysis of alpine high pressure ophiolite hosted pseudotachylyte corsica france
Journal of Structural Geology, 2016Co-Authors: Remi Magott, Olivier Fabbri, Marc FournierAbstract:Pseudotachylyte in the Cima di Gratera ophiolite, Alpine Corsica, is distributed in the peridotite unit and in the overlying Metagabbro unit and was formed under blueschist to eclogite metamorphic facies conditions, corresponding to a 60–90 km depth range. Peridotite pseudotachylyte is clustered in fault zones either beneath the tectonic contact with overlying Metagabbros or at short distance from it. Fault zones are either parallel to the contact or make an angle of 55° to it. Displacement sense criteria associated with fault veins indicate top-to-the-west or top-to-the-northwest reverse senses. Cataclasite flanking most veins was formed before or coevally with frictional melting and likely mechanically weakened the peridotite, facilitating subsequent seismic rupture. In the basal part of the Metagabbro unit, post-mylonitization pseudotachylyte can be distinguished from pre-mylonitization pseudotachylyte formed earlier. In the equant Metagabbro above the mylonitic sole, only one episode of pseudotachylyte formation can be identified. Kinematics associated with Metagabbro pseudotachylyte remain unknown. The geometry and kinematics of the pseudotachylyte veins from the peridotite unit and to a lesser extent from the Metagabbro unit are similar to modern seismic ruptures of the upper parts of the Wadati-Benioff zones such as in the Pacific plate beneath NE Japan.
Olivier Fabbri - One of the best experts on this subject based on the ideXlab platform.
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Polyphase ductile/brittle deformation along a major tectonic boundary in an ophiolitic nappe, Alpine Corsica: Insights on subduction zone intermediate-depth asperities
Journal of Structural Geology, 2017Co-Authors: Remi Magott, Olivier Fabbri, Marc FournierAbstract:In an ophiolitic nappe of Alpine Corsica, a major fault zone superimposes Metagabbro over serpentinite and peridotite. Ductile and brittle deformation structures are observed in the fault damage zones. In the Metagabbro damage zone, early deformation culminates in blueschist or eclogite facies conditions and consists of west-verging mylonitization alternating with pseudotachylyte-forming faulting with undetermined vergence. This early deformation is likely coeval with west-verging seismic (pseudotachylyte-forming) reverse faulting in the footwall peridotite or with aseismic distributed cataclastic deformation of footwall serpentinite. These early events (aseismic mylonitization or distributed cataclasis and seismic faulting) are interpreted as reverse faulting/shear in an east-dipping subducting oceanic lithosphere in Cretaceous to Eocene times. Late deformation events consist of ductile shear and seismic faulting having occurred under retrograde greenschist conditions. Kinematics of the ductile shear is top-to-the-east. These events are interpreted as the result of syn-to post-collision extension of Alpine Corsica in Eocene to Miocene times. The heterogeneous distribution of pseudotachylyte veins along the fault zone (abundant at peridotite-Metagabbro interfaces, rare or absent at serpentinite-Metagabbro interfaces) is interpreted as the consequence of contrasted frictional properties of the rocks in contact. High-friction peridotite-Metagabbro contacts could correspond to asperities whereas low-friction serpentinite-Metagabbro contacts could correspond to creeping zones.
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polyphase ductile brittle deformation along a major tectonic boundary in an ophiolitic nappe alpine corsica insights on subduction zone intermediate depth asperities
Journal of Structural Geology, 2017Co-Authors: Remi Magott, Olivier Fabbri, Marc FournierAbstract:In an ophiolitic nappe of Alpine Corsica, a major fault zone superimposes Metagabbro over serpentinite and peridotite. Ductile and brittle deformation structures are observed in the fault damage zones. In the Metagabbro damage zone, early deformation culminates in blueschist or eclogite facies conditions and consists of west-verging mylonitization alternating with pseudotachylyte-forming faulting with undetermined vergence. This early deformation is likely coeval with west-verging seismic (pseudotachylyte-forming) reverse faulting in the footwall peridotite or with aseismic distributed cataclastic deformation of footwall serpentinite. These early events (aseismic mylonitization or distributed cataclasis and seismic faulting) are interpreted as reverse faulting/shear in an east-dipping subducting oceanic lithosphere in Cretaceous to Eocene times. Late deformation events consist of ductile shear and seismic faulting having occurred under retrograde greenschist conditions. Kinematics of the ductile shear is top-to-the-east. These events are interpreted as the result of syn-to post-collision extension of Alpine Corsica in Eocene to Miocene times. The heterogeneous distribution of pseudotachylyte veins along the fault zone (abundant at peridotite-Metagabbro interfaces, rare or absent at serpentinite-Metagabbro interfaces) is interpreted as the consequence of contrasted frictional properties of the rocks in contact. High-friction peridotite-Metagabbro contacts could correspond to asperities whereas low-friction serpentinite-Metagabbro contacts could correspond to creeping zones.
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subduction zone intermediate depth seismicity insights from the structural analysis of alpine high pressure ophiolite hosted pseudotachylyte corsica france
Journal of Structural Geology, 2016Co-Authors: Remi Magott, Olivier Fabbri, Marc FournierAbstract:Pseudotachylyte in the Cima di Gratera ophiolite, Alpine Corsica, is distributed in the peridotite unit and in the overlying Metagabbro unit and was formed under blueschist to eclogite metamorphic facies conditions, corresponding to a 60–90 km depth range. Peridotite pseudotachylyte is clustered in fault zones either beneath the tectonic contact with overlying Metagabbros or at short distance from it. Fault zones are either parallel to the contact or make an angle of 55° to it. Displacement sense criteria associated with fault veins indicate top-to-the-west or top-to-the-northwest reverse senses. Cataclasite flanking most veins was formed before or coevally with frictional melting and likely mechanically weakened the peridotite, facilitating subsequent seismic rupture. In the basal part of the Metagabbro unit, post-mylonitization pseudotachylyte can be distinguished from pre-mylonitization pseudotachylyte formed earlier. In the equant Metagabbro above the mylonitic sole, only one episode of pseudotachylyte formation can be identified. Kinematics associated with Metagabbro pseudotachylyte remain unknown. The geometry and kinematics of the pseudotachylyte veins from the peridotite unit and to a lesser extent from the Metagabbro unit are similar to modern seismic ruptures of the upper parts of the Wadati-Benioff zones such as in the Pacific plate beneath NE Japan.
Samuel Angiboust - One of the best experts on this subject based on the ideXlab platform.
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Intermediate-depth brecciation along the subduction plate interface (Monviso eclogite, W. Alps)
Lithos, 2018Co-Authors: Michele Locatelli, Anne Verlaguet, Philippe Agard, Laura Federico, Samuel AngiboustAbstract:Abstract The Monviso meta-ophiolite complex (Northern Italy, Western Alps) represents an almost intact fragment of Tethyan oceanic lithosphere metamorphosed at ~80 km depth (~2.6GPa–550 °C) during the Alpine subduction. We focus our study on a major shear zone cutting across this slab fragment at low angle (the Lower Shear Zone; LSZ). Here, in its talc and tremolite-rich serpentinite matrix, are embedded (together with metasedimentary lenses) variously brecciated Fe-Ti and Mg-Al Metagabbro blocks. The latter were either interpreted as eclogitic breccias resulting from intermediate-depth rupture or as inherited, overprinted oceanic core complex features. Our new field, structural and petrographic data testify the genesis of this Metagabbro breccia blocks at eclogite-facies conditions. Three types of eclogitic blocks can be distinguished, with non-random distribution (and decreasing size from top to base) throughout the ~200-m-thick and ~15 km-long LSZ: (1) Fe-Ti-Metagabbros, brecciated and scattered in the upper to intermediate levels of the LSZ; (2) meter-size blocks and decameter-scale slivers of intact Mg-Al Metagabbros, locally brecciated; (3) dm- to m-scale blocks of intact Fe-Ti Metagabbros without breccia fabrics. Brecciation at eclogite facies conditions (at ~80 km depth) is documented by: i) the eclogitic foliation of intact Mg-Al-rich Metagabbros (composed of omphacite + clinozoisite ± rutile and locally garnet) cut by breccia planes (cemented by omphacite + garnet ± lawsonite) and ii) the occurrence in breccia clasts of minerals that are fractured and offset along peak P-T omphacite-bearing planes. Rupture preferentially affected the Fe-Ti Metagabbros, suggesting that rheological contrasts controlled the locus of brecciation. The occurrence of a first omphacite-rich matrix (M1, ~2.7GPa - 580 °C) crosscut by omphacite + garnet-bearing matrix M2 (~2.4GPa - 560 °C), witnesses multiple brittle rupture events, prior to a stage of eclogite facies fluid ingression marked by massive lawsonite recrystallization (matrix M3).
Eberhard Seidel - One of the best experts on this subject based on the ideXlab platform.
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Magmatic and metamorphic evolution of Metagabbros in the Münchberg Massif, N.E. Bavaria
Contributions to Mineralogy and Petrology, 1991Co-Authors: D. Bosbach, H.-g. Stosch, Eberhard SeidelAbstract:The central gneiss complex of the Munchberg Massif consists of the Liegendserie at the base and the Hangendserie at the top. Metagabbros are found in the Liegendserie; eclogites occur in the Hangendserie. New isotope data revive the discussion whether a genetic relationship exists between Metagabbros and eclogites in the Munchberg Massif. It is possible to relate the two types of rocks to the same protoliths by variable degrees of crustal contamination and magmatic accumulation. Therefore, a common magmatic origin may be assumed. Both the Metagabbros and the eclogites were affected by amphibolite-facies metamorphism. The amphibolitization of the Metagabbros was a prograde metamorphic event. Increasing temperature is indicated by inverse zonation of recrystallized plagioclase and increasing Mg/Fe ratios in garnet from core to rim. Geothermobarometry yields a temperature of 600°C and a pressure of about 11 kbar for the peak of metamorphism. In contrast, the eclogites underwent a first high-pressure stage at a minimum pressure of 14 kbar and a temperature estimated at 600°C and were subsequently overprinted under amphibolite-facies conditions at 10 kbar/700°C. A common magmatic origin of Metagabbros (Liegendserie) and eclogites (Hangendserie) of the Munchberg Massif can no longer be discarded. However, the converging P-T-t paths reflect a different geodynamic evolution of the Liegendserie and the Hangendserie after magmatism and before amphibolite-facies metamorphism.